Polyethylene is widely used to prepare food packaging films and bags such as cereal liners and cake mix bags, grocery bags, stretch-wraps, shrink-wraps, garbage can liners, and shipping bags. Some applications, such as food packaging films and bags, require films to have sufficient water vapor and oxygen barrier properties to preserve the contents. The packaging films usually have a multilayer structure. Depending on the intended application, the number, type, and arrangement of layers employed will vary. Ethylene-vinyl alcohol (EVOH) copolymers and polyamides (nylons) are often used as barrier layers. Polyethylene is often used as one or more layers.
High density polyethylene (HDPE) is often used as a layer in the multilayer films because of its high strength and modulus. HDPE can be nucleated. Nucleated HDPE has improved water vapor barrier property. Thus when nucleated HDPE is used as a layer in a multilayer film, it provides the film not only with physical strength but also with increased barrier to water vapor. One problem associated with the use of nucleated HDPE in a multilayer film is that nucleated HDPE causes the multilayer films to curl to a greater extent. The curling brings inconvenience to the film manufacturers and consumers. Therefore, there is a need to reduce or eliminate the curling of multilayer film caused by the use of nucleated HDPE.